Previous studies have demonstrated that the incidence and severity of respiratory virus infections is greater in smokers than in non-smokers, but the mechanisms mediating these responses are currently not well understood. Our preliminary data demonstrate that cultured nasal epithelial cells from smokers are more susceptible to influenza virus infections, shed more virus, and have decreased expression of type 1 interferons. This in vitro model thus provides an important tool to investigate the cellular and molecular basis for enhanced susceptibility to influenza virus seen in smokers. In addition, our preliminary data demonstrate that nasal administration of live attenuated influenza virus (LAIV) offers the possibility of studying influenza virus infections safely in humans in vivo. Using tightly linked human in vitro and in vivo approaches, this proposal is designed to test the hypothesis that chronic exposure to cigarette smoke alters epithelial antiviral and inflammatory responses to influenza virus infection via two potentially related mechanisms: decreased expression of phase II (antioxidant) enzymes and suppression of type 1 interferon (antiviral) pathways. We further hypothesize that upregulation of phase II enzymes via nutritional supplementation with SFN is a potential therapeutic strategy to mitigate these effects. Specific aim 1 will use an in vitro model of differentiated human nasal epithelial cells to determine mechanisms that modify influenza-induced antiviral defense responses in smokers, initially focusing on the role of type I IFN antiviral defense responses and the potential role of cigarette smoke-induced gene silencing. Specific aim 2 will use our existing protocol of administration of LAIV vaccine as a model for influenza virus infections to confirm mechanisms that mediate enhanced susceptibility to influenza infections in smokers in vivo. LAIV-induced viral replication and antiviral defense responses will be assessed in smokers and non-smokers using endpoints measured in nasal biopsy tissue and lavage fluids. Outcomes within each study cohort will be grouped based on changes in innate immune defense gene expression found in specific aim 1. Specific aim 3 will use both the in vitro and in vivo models to determine the relationships between antioxidant gene expression, antiviral pathways, and virus-induced inflammation in smokers and non-smokers. We will assess how upregulation of HO-1 as a result of supplementation with SFN can improve key abnormalities in antiviral pathways and inflammatory/immune response changes associated with smokers, as identified in SA1+2. Data derived from these studies will yield insights into the mechanisms that enhance the susceptibility to influenza virus infections in smokers and explore potential therapeutic interventions using a translational research design.